1. Field of the Invention
The present invention relates to a holding apparatus and a holding method, and an exposure apparatus which uses a mask and a substrate held by the holding apparatus to expose a mask pattern onto the substrate. More specifically, the present invention relates to a holding apparatus and a holding method, an exposure apparatus and a device manufacturing method, suitable for use in a lithography process, particularly when devices such as liquid crystal display elements and semiconductor elements are manufactured.
2. Background Art
In the lithography process, being one of the manufacturing processes for semiconductor devices, various kinds of exposure apparatus have been used, which transfer a circuit pattern formed on a mask or a reticle (hereinafter referred to as a “reticle”) onto a substrate such as a wafer or a glass plate, to which a resist (photosensitizer) has been applied. For example, as an exposure apparatus for semiconductor devices, a reduced size projection exposure apparatus is mainly used, which transfers the reticle pattern onto the wafer while reducing the size of the pattern, using a projection optical system, corresponding to the miniaturization of the minimum line width of the pattern (device rule) accompanying recent high integration of integrated circuits.
In the above described exposure apparatus, when the reticle pattern is transferred onto the wafer, the reticle is held on a reticle holder by vacuum attraction. As a conventional example of such a reticle holder, there is one shown in FIG. 26. FIG. 26 is a perspective view illustrating a reticle holder for holding a reticle. As shown in this figure, the reticle holder 100 comprises an opening 102 formed at the center, seat portions 104 provided at a plurality of positions (three places) on the upper face, and suction pads 106 respectively provided on the upper faces of the seat portions 104. The reticle holder 100 is provided so as to be movable two-dimensionally in XY directions with respect to a base 110. The suction pads 106 are provided at positions facing the lower face of the reticle R, and connected to a compressor (suction apparatus) which is not shown. The compressor draws out gas in the space between the lower face of the reticle R and the suction pads 106 to make the pressure in the space between the lower face of the reticle R and the suction pads 106 lower than the outside pressure, so that the reticle R is attracted and held by the reticle holder 100.
The reticle R has a pattern at the center on the lower face, and a pellicle PE for protecting a pattern face is provided on the pattern face (that is, the central part on the lower face of the reticle R). Therefore, the reticle holder 100 should attract and hold the portions of the lower face of the reticle, except of the portion where the pellicle PE is provided.
It is preferable that the contact surface between the suction pads 106 of the reticle holder 100 and the reticle R is large, in order that the reticle holder 100 stably holds the reticle R. However, as described above, the size (area) of the face of the reticle R which is attracted by the reticle holder 100 is restricted by the pellicle PE. If it is tried to attract and hold a wide area of the portion other than the pellicle PE, on the lower face of the reticle R, even an area, which does not have a predetermined surface precision, for example, an outer peripheral area on the lower face of the reticle R (hereinafter referred to as “precision unwarrantable area”) must be attracted and held by the reticle holder 100. In this case, the contact surface of the reticle R with respect to the suction pads 106 is distorted, and this distortion affects even the area having predetermined surface precision (hereinafter referred to as a “precision warrantable area”) to decrease the surface precision, thereby causing a problem in that high precision exposure processing cannot be performed.
On the other hand, it can be considered to attract and hold the area in the vicinity of the pellicle PE (hereinafter referred to as an “inside edge area”), being the precision warrantable area, in the portion other than the pellicle PE on the lower face of the reticle R. However, when the reticle holder 100 holds this inside edge area, the reticle holder 100 interferes with a carrier device which loads and unloads the reticle R with respect to the reticle holder 100, which is not desirable. In other words, when the reticle R is loaded or unloaded with respect to the reticle holder 100, a carrier device having a fork portion is used. However, when the reticle R is supported by this fork portion, the fork portion supports the portion other than the pellicle PE on the lower face of the reticle R. When the reticle R is loaded or unloaded with respect to the reticle holder 100 by using this carrier device, the shape or the size of the seat portion 104 of the reticle holder 100, or the position or the size of the suction pads 106 are restricted, in order to prevent interference between the reticle holder 100 and the fork portion, and as a result, the position and size of the surface to which the reticle R is attracted are also restricted.
Moreover, it can be also considered to attract and hold only the precision warrantable area existing in an area where interference with the carrier device does not occur, which is the portion other than the pellicle PE on the lower face of the reticle R. However, in this case, since the surface of the reticle R to be attracted becomes small, the holding power of the reticle holder 100 with respect to the reticle R becomes weak. For example, when the reticle holder 100 is shifted with respect to the base 110 at high speed, there is the possibility that the reticle R on the reticle holder 100 is deviated due to the inertia force. When the surface of the reticle R to be attracted is small, it can be considered to increase the attractive force by the compressor, to increase the holding power with respect to the reticle R. However, in this case, since a local force acts on the reticle R, the reticle R may be distorted.
In view of the above situation, it is an object of the present invention to provide a holding apparatus and a holding method that can hold a reticle (mask) stably, without deteriorating the surface precision in the precision warrantable area, and an exposure apparatus that can perform accurate exposure processing with this holding apparatus, and a device manufacturing method that can manufacture devices highly accurately.